1. Field
Embodiments of the invention relate to the field of network processing; and more specifically to emergency call processing in a distributed session border controller (SBC) system.
2. Background
A distributed session border controller (SBC) system includes a signaling SBC (S-SBC) and a data SBC (D-SBC). The S-SBC controls the opening, closing, and policing of traffic flows through the D-SBC through a standard interface (e.g., the Ia interface defined by ETSI (European Telecommunications Standards Institute) TISPAN (Telecommunications and Internet converged Services and Protocols for Advanced Networking) which uses the H.248 control protocol (“Gateway control protocol: Version 3”, ITU-T Recommendation H.248.1, September 2005). H.248 messages are transmitted between the S-SBC and the D-SBC.
Emergency calls (e.g., 911 calls or other local emergency numbers) that are received by the S-SBC are processed at the highest priority. Similarly, the D-SBC processes emergency calls at a high priority. In order to process the emergency calls at a high priority, the S-SBC and the D-SBC need to determine that the call is an emergency call. Typically, the S-SBC determines whether a call is an emergency call by performing number analysis on the dialed number (e.g., determining whether the dialed number is an emergency number). After determining the call is an emergency call, the S-SBC transmits a H.248 add message to the D-SBC, the add message including an emergency indicator token (the H.248 protocol defines the emergency indicator token). The D-SBC receives the H.248 add message and parses the H.248 message to extract the emergency indicator token. Until extracting the emergency indicator token, the D-SBC does not give high priority to that emergency call.